1. Field of the Invention
The present invention relates to an image reading apparatus and a control method.
2. Description of the Related Art
Conventionally, there are image reading apparatuses including a contact image sensor (CIS) as a reading device. The CIS is a sensor having a number of photoelectric conversion elements arranged in the main scanning direction. The number of photoelectric conversion elements corresponds to the number of pixels that are read. For example, if the direction of the short side of a document is considered as the main scanning direction, a CIS capable of reading an A4 size document has the photoelectric conversion elements for approximately 5100 pixels if the resolution is 600 dpi (dots per inch).
Image data for one line of a document read by such photoelectric conversion elements is converted photoelectrically, and then sequentially output in synchronization with a clock signal (hereinafter referred to as a sensor clock signal) input in the CIS. Thus, the time necessary in reading out one line of a document will be a time for which a number of transfer clock signals corresponding to the number of pixels are input in the CIS. In most cases, the transfer clock of the CIS is set to a low frequency (about 5 MHz) due to structural reasons. Thus, the CIS is generally used for reading apparatuses that operate at a relatively low speed.
Attempts for applying the CIS to high speed reading apparatuses are being proposed. For example, a reading apparatus that allows faster reading time by setting a plurality of photoelectric conversion elements arranged in a plurality of image reading regions in the main scanning direction as one element group and parallelly outputting image data from each element group has been proposed. In this case, if one line is divided into three in the main scanning direction, image data can be parallelly output from three element groups. Thus, the read out time of the image data will be one third of that for one line.
However, even if a CIS capable of parallel reading is used, rearrangement of the image data is necessary. This is because the image data needs rearrangement so that it is continuous in the main scanning direction. The rearrangement is performed by temporarily storing the image data, which is discontinuous in the main scanning direction, at an appropriate address of a storage medium, such as a memory, and then reading it out. The rearrangement is also performed by storing the input image data, which is discontinuous in the main scanning direction, in a storage medium, such as a memory, in the order the image data is input, and reading it out in such an order that the image data is continuous in the main scanning direction (e.g., Japanese Patent Application Laid-Open No. 2007-13595, Japanese Patent Application Laid-Open No. 9-130592, and Japanese Patent Application Laid-Open No. 2004-220585). However, if a storage medium such as a memory is necessary, it will raise the cost of the reading apparatus.
According to Japanese Patent Application Laid-Open No. 9-130592, rearrangement of the image data and image processing are performed by one memory in the reading apparatus so as to reduce the memory capacity necessary in rearranging the image data that is discontinuous in the main scanning direction. Further, Japanese Patent Application Laid-Open No. 2004-220585 discusses a technique that uses a storage medium, outside of an integrated circuit, having a relatively large capacity and rearranges the image data using a direct memory access controller (DMAC) before the image processing is performed by the reading apparatus.
However, each of the above-described conventional techniques requires a storage medium used for temporarily storing the image data that is discontinuous in the main scanning direction in rearranging the data. This raises the cost of the image reading apparatus.